In the field of printing, the most common type printer has been the printer which impacts against record media that is moved past a printing line or line of printing. As is well-known, the impact printing operation depends upon the movement of impact members, such as print hammers or wires or the like, which are typically moved by means of an electromechanical drive system and which system enables precise control of the impact members.
In the field of dot matrix printers, it has been quite common to provide a print head which has included therein a plurality of print wire actuators or solenoids arranged or grouped in a manner to drive the respective print wires a very short, precise distance from a rest or non-printing position to an impact or printing position. The print wires are generally either secured to or engaged by the solenoid plunger or armature which is caused to be moved such precise distance when the solenoid coil is energized and wherein the plunger or armature normally operates against the action of a return spring.
It has also been quite common to provide an arrangement or grouping of such solenoids in a circular configuration to take advantage of reduced space available in the manner of locating the print wires in that specific area between the solenoids and the front tip of the print head adjacent the record media. In this respect, the actuating ends of the print wires are positioned in accordance with the circular arrangement and the operating or working ends of the print wires are closely spaced in vertically aligned manner adjacent the record media. The availability of narrow or compact actuators permits a narrower or smaller print head to be used and thereby reduces the width of the printer because of the reduced clearance at the ends of the print line. The print head can also be made shorter because the narrow actuators can be placed in side-by-side manner closer to the record media for a given amount of wire curvature.
In the wire matrix printer which is utilized for receipt and journal printing operation, the print head structure may be a multiple element type and horizontally disposed with the wire elements aligned in a vertical line and supported on a print head carriage which is caused to be moved or driven in a horizontal direction for printing in line manner across the receipt or journal paper and wherein the drive elements or transducers may be positioned in a circular configuration with the respective wires leading to the front tip of the print head. In another arrangement of a wire matrix printer which is utilized for business forms or like record media printing operation, the print head may be oriented in a manner wherein the nose is pointed downward for printing on the form, slip or like media while the carriage and print head are moved above and across the form or media in the horizontal direction.
Further, the printer structure may be an arrangement which includes a plurality of equally-spaced, horizontally-aligned, single element print heads which are moved in back and forth manner to print successive lines of dots in making up the lines of characters. In this latter arrangement, the drive elements or transducers are individually supported along a line of printing. Dependent upon the printer type, the horizontally-aligned, single element print heads may be either horizontally or vertically oriented in the axial direction for printing operation. These single wire actuators or solenoids are generally tubular or cylindrically shaped and include a shell which encloses a coil, an armature and a resilient member arranged in manner and form wherein the actuator is operable to cause the print wire to be axially moved a small precise distance in dot matrix printing.
In the case of a wire matrix printer which is utilized for form or multi-copy printing, the difference in thickness of the forms or copies may require some means or mechanism for adjusting the gap or increasing the distance between the print head and the printer platen. It is in the field of business forms or like record media of different thicknesses that the subject matter of the present invention is most closely associated and which provides for improved and advantageous positioning and control of such forms during the printing operation. It is desirable that a positive method of forms compensation be provided regardless of the thickness of the form.
Representative documentation in the field of wire matrix print heads used for printing forms or like record media includes U.S. Pat. No. 2,839,176, issued to A. W. Metzner et al. on June 17, 1958, which discloses an adjustable platen roll which is supported at each end by a pin wheel body that is rotatably mounted on a bearing in the form of a bushing having a cylindrical enter surface and an eccentric bore.
U.S. Pat. No. 3,154,184, issued to R. R. Gallant et al. on Oct. 27, 1964, discloses platen adjusting means for typewriters wherein the platen is seated upon saddlers of part-circular saddle elements each of which have a peripheral face in an eccentric relationship to the centers of the saddlers.
U.S. Pat. No. 3,461,797, issued to A. C. Trab et al. on Aug. 19, 1969, discloses an eccentrically mounted platen structure in selective printing machines wherein the platen is eccentrically journaled in a pair of continuously rotating end disks so as to perform a cycloidal motion parallel to itself under control of a planetary gear system of the same eccentricity.
U.S. Pat. No. 3,912,068, issued to O. Kwan et al. on Oct. 14, 1975, discloses a printer having a document thickness compensating device wherein the spring-mounted platen is moved into position to clamp the document with substantially uniform pressure against elongated surfaces, and a document holding assembly includes a slot with control of document movement to position the document for printing.
U.S. Pat. No. 4,024,940, issued to W. Hendrischk et al. on May 24, 1977, discloses a matrix printer having a document thickness compensating device wherein a roller on the print head runs on a resilient rail urged against the platen and the roller can be retracted by pivoting the rail carrier under engagement of a second rail cooperating with a second roller on the head.
U.S. Pat. No. 4,143,977, issued to T. Kurihara on Mar. 13, 1979, discloses first and second independently movable platen units arranged to compensate for recording medium thickness, a third platen unit between the first and second units, and first and second springs secured to the first and second units and biasing the third unit toward the print station.
U.S. Pat. No. 4,184,780, issued to T. Kurihara et al. on Jan. 22, 1980, discloses a printer having a platen with separate units movable toward and away from the recording medium by rotary cams and spring means and lockable in position by lever means.
U.S. Pat. No. 4,189,244, issued to G. F. Harrison on Feb. 19, 1980, discloses a platen gap adjuster that has a shaft with offset spindles on a common axis so that rotation of the spindles about the axis causes eccentric rotation of the shaft to displace the print head.
U.S. Pat. No. 4,210,076, issued to Y. Yamamoto et al. on July 1, 1980, discloses printing apparatus with a type carrier movable on a tiltable support structure, position retaining means for the structure, clearance adjusting means depending upon printing medium thickness and cam means providing intervention between the retaining means and the adjusting means.
U.S. Pat. No. 4,222,673, issued to M. G. Plaza et al. on Sept. 16, 1980, discloses a print head carriage having a rotatable manifold member operating in eccentric camming manner to adjust the distance between the print head and the platen for accommodating printing media of various thicknesses.
U.S. Pat. No. 4,227,819, issued to R. F. Manriquez on Oct. 14, 1980, discloses a platen assembly for feeding and holding single or multi-layer record media and having one of a pair of feed rollers pivotally mounted to yieldingly engage and hold both sides of the record media while the platen yieldingly engages and holds the record media against gap determining guides. The platen is free floating with the aid of a pair of coil springs and is raised into engagement with the record media by rotatable cam means.
U.S. Pat. No. 4,422,782, issued to R. L. Lawter et al. on Dec. 27, 1983, discloses a record member feed and support mechanism wherein a control solenoid moves record member drive rollers and a spring urged platen member. Force on the platen compensates for thickness of the record member and spring means are associated with the drive rollers to hold the record member in position.
U.S. Pat. No. 4,514,101, issued to H. E. Smith on Apr. 30, 1985, discloses paper thickness adjusting mechanism including a pair of guide rails and an adjustable marking module movable along the rails. The mechanism uses a toggle bracket to allow the module to pivot about the guide rail relative to the platen.
U.S. Pat. No. 4,589,784, issued to F. Valle on May 20, 1986, discloses a point of sale printer wherein a receipt is guided between the print head and a part of width of the platen and a slip is also guided over the platen. Other documents may be fed upwardly or downwardly between guides and past the print head.
And, U.S. Pat. No. 4,632,577, issued to R. A. Brull et al. on Dec. 30, 1986, discloses record media thickness compensating mechanism wherein the platen is movable toward and away from the print head and the mechanism uses first and second cam members to control the position of the platen.